The performance of an integrated circuit (IC) typically depends on several parameters that influence the speed at which the IC operates. Three such parameters of the IC are its supply voltage, operating temperature, and the thickness of the transistor-gate oxides. Variations in these parameters from respective nominal values may affect the delay time of signals that propagate within the IC, and thus, may vary the operating speed of the IC from a nominal speed. For example, if the voltage supply is lower than the nominal value, logic gates within the IC may operate more slowly because the rise times between logic 0 and logic 1 are longer due to the lower drive signal strength. Similarly, as the temperature of the IC decreases, logic circuits within the IC operate more quickly due to the increased mobility of carriers in the transistors. In addition, the thinner the gate-oxides, the faster the transistors, and thus, the faster the logic circuits of the IC. Conversely, the higher the supply voltage, the more quickly the logic gates operate, and the higher the temperature or the thicker the gate-oxides, the more slowly the logic gates operate.
Because these parameters may vary, the IC manufacturer typically accommodates these variations by predicting a best-case scenario and a worst-case scenario and designing the IC for a nominal case that is between the best- and worst-case scenarios. In a best-case scenario, the voltage supply is at its highest rated level, the IC operates at its lowest rated temperature, and the manufacturing process parameters (e.g., gate-oxide thickness) have their “fastest” values, such that the IC operates at its highest speed. Conversely, in the worst-case scenario, the voltage supply is at its lowest rated level, the temperature of the IC is at its highest rated value, and the manufacturing-process parameters have their “slowest” values, such that the IC operates at its slowest speed. By predicting the worst-case parameter values, an engineer can typically design an IC to operate adequately even under worst-case conditions.
However, it is becoming more difficult to design an IC to operate properly over the wide range of worst-case and best-case conditions, and soon may not be feasible. As ICs become increasingly dense (i.e., more transistors per unit area), there is more available area in which to include new forms of compensation circuitry. Supply voltage and temperature are currently controlled by circuits or devices that are external to the IC. IC process characteristics are typically universally ignored, except at the time of the original manufacturing tests.
Accordingly, a need exists for a way to more accurately compensate for the affect that parameter variations have on the operation of an IC.